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Publication numberUS4184750 A
Publication typeGrant
Application numberUS 05/899,274
Publication dateJan 22, 1980
Filing dateApr 24, 1978
Priority dateNov 12, 1976
Publication number05899274, 899274, US 4184750 A, US 4184750A, US-A-4184750, US4184750 A, US4184750A
InventorsAllen Bloom, Ling K. Hung
Original AssigneeRca Corporation
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Novel liquid crystal dyestuffs and electro-optic devices incorporating same
US 4184750 A
Abstract
Novel liquid crystal dyestuffs of the formula ##STR1## wherein Y and Z are different and can be nitro or cyano and --N(R)2 wherein R is alkyl or alkylene, preferably of 1 to 4 carbon atoms, and X can be hydrogen, methyl, fluoro or chloro, can be added to known liquid crystal compositions to impart color to the mixtures and improve contrast in a liquid crystal electro-optic device containing such mixtures.
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Claims(6)
What is claimed is:
1. In an electro-optic device comprising a nematic liquid crystal composition with a positive dielectric anisotropy between two electrodes, the improvement which comprises the addition to the liquid crystal composition of a liquid crystal dyestuff of the formula: ##STR17## wherein Y and Z are different one is nitro or cyano and the other is --N(R)2 wherein R is alkyl or alkylene, of 1 to 8 carbon atoms, and X can be hydrogen, methyl, fluoro or chloro.
2. A device according to claim 1 wherein Y is a nitro group and Z is a --N(R)2 group.
3. A device according to claim 1 wherein Y is a cyano group and Z is a --N(R)2 group.
4. A device according to claim 1 wherein R is an alkyl group of 1 to 4 carbon atoms.
5. A device according to claim 2 wherein X is methyl.
6. A device according to claim 3 wherein X is methyl.
Description

This is a division of application Ser. No. 741,538, filed Nov. 12, 1976, now U.S. Pat. No. 4,105,654, issued Aug. 8, 1978.

This invention relates to novel liquid crystal devices. More particularly, this invention relates to liquid crystal mixtures and devices containing novel liquid crystalline dyes.

BACKGROUND OF THE INVENTION

Electro-optic devices containing liquid crystal compounds have become commercially important recently because of their low power requirements and good contrast, particularly for applications such as watch faces, calculator displays and the like. Although liquid crystal compounds have been known for many years, the discovery of nematic liquid crystals having a mesomorphic transition temperature range that spans room temperature sparked a renewed interest in these materials and greatly expanded their marketability. Research is continuing to discover new room temperature liquid crystal compounds and mixtures of liquid crystal compounds having improved contrast in electro-optic devices.

SUMMARY OF THE INVENTION

We have discovered novel liquid crystal dye compounds, 4"-cyano- or 4"-nitro-benzylidene-4'-(N,N-dialkylamino)-4-aminoazobenzenes. These liquid crystals, when admixed in small amounts with low melting liquid crystal materials, impart strong colors to the mixtures, but without materially affecting the transition temperature range of the liquid crystal composition to which they are added. The present dyes thus improve the contrast of electro-optic devices employing these liquid crystal materials, and impart decorative colors in the orange to red to brown hues, without adversely affecting other properties of the liquid crystals.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a cross-sectional view of an electro-optic device embodying the invention.

DETAILED DESCRIPTION OF THE INVENTION

The novel liquid crystal dyes of the present invention have the formula: ##STR2## wherein Y and Z are different and can be nitro or cyano and --N(R)2 wherein R is alkyl or alkylene of 1-8, preferably of 1 to 4 carbon atoms, and X can be hydrogen, methyl, fluoro or chloro.

These dyes encompass a rather broad spectrum of mesomorphic temperature ranges and have deep colors. They can be admixed with lower melting liquid crystal compositions in small amounts to impart color to the liquid crystals so that cells including them exhibit improved contrast.

The above-described liquid crystalline dyes can be prepared by reacting an appropriate benzaldehyde and a suitable aminoazobenzene or substituted derivative thereof in solution. Para-toluenesulfonic acid can be employed as a catalyst. The product is isolated and purified in known manner, as by recrystallization or column chromatographic techniques.

The dyes can be admixed with nematic liquid crystal compositions to impart a color characteristic of each dye. Low melting nematic liquid crystal compositions, particularly p-alkoxybenzylidene-p'-alkylanilines and their mixtures with other liquid crystals, and mixture of p-alkoxy- or p-acyloxybenzylidene-p'-cyanoanilines, or mixtures of p-cyanophenyl-p'-alkylbenzoates and p-phenylene-2,4-dialkylbenzoates have a transition temperature range that includes room temperature, and are particularly suitable. The exact amount of dye to be added depends on the solubility of the dye in the liquid crystal composition and also on the color desired. In general, from about 0.05% up to about 2% by weight of the dyestuff in the liquid crystal mixture, and preferably from about 0.2% to 0.4% by weight of the dyestuff, will be employed.

P-alkoxybenzylidene-p'-butylanilines are known liquid crystals and are described for example in U.S. Pat. No. 3,829,491 which issued Aug. 13, 1974 to Strebel. Mixtures of p-methoxybenzylidene-p'-butylaniline (hereinafter referred to as MBBA) and p-ethoxybenzylidene-p'-n-butylaniline (hereinafter referred to as EBBA) have particularly broad and low use temperature ranges. Mixtures containing about 35 to about 70% by weight of MBBA are preferred.

P-alkoxybenzylidene-p'-cyanoanilines are also known and are described in U.S. Pat. No. 3,499,702, issued Mar. 10, 1970, to Goldmacher et al. A mixture containing 85% by weight of a 70:30 molar ratio of MBBA and EBBA and 15% by weight of p-ethoxybenzylidene-p'-aminobenzonitrile has been disclosed by H. A. Tarry, Services Electron Research Laboratory Technical Journal, Vol. 23, No. 1, 1973. P-acyloxybenzylidene-p'-cyanoanilines have been disclosed by Castellano in U.S. Pat. No. 3,597,044.

In preparing an electro-optic device, the liquid crystal compounds should be rigorously purified to remove ionic and nonionic impurities which may react to degrade the liquid crystal compounds either by decomposition, transubstitution reactions and the like. For commercially acceptable cells, the liquid crystal compounds should be purified so that their resistivity is 11011 ohm-cm or higher.

After the desired liquid crystal compounds are mixed together, a small amount of a chiral aligning agent is advantageously added. The aligning agent serves to orient the molecules of the mixture in the same direction since chiral compounds normally twist in a right-handed or left-handed direction. Suitable aligning agents include cholesteryl derivatives, such as cholesteryl halides, cholesteryl esters and the like; optically active compounds such as d- or 1-α-pinene, d- or 1-octanol and chiral esters such as 4-propylphenyl-4'-(4"-2-methylbutylphenylcarboxy)-2-chlorobenzoate having the formula ##STR3## and the like. The amount of the chiral aligning agent added is not critical, but in general from about 0.05 to about 2.0% by weight of the liquid crystal composition is suitable, providing the mixture remains nematic.

Referring to the FIGURE, a liquid crystal cell is constructed from two glass plates 2 and 4 having conductive indium-doped tin oxide coatings as electrodes 6 and 8, respectively, on facing surfaces thereof. Thin silicon oxide layers 10 and 12 are evaporated onto the conductive layers 6 and 8, respectively, at an angle of 60 degrees. These layers act to align the liquid crystal material. One-half mil (25.4 microns) thick glass frit spacers 14 and 16 maintain the coated glass plates 2 and 4 apart to complete the cell components. The cell is baked at 525 C. to melt the glass frit and seal the cell except for a single fill port. The cell is filled with the desired liquid crystal composition 18 in the isotropic state and hermetically sealed with a solder.

The invention will be further illustrated by the following Examples but it is to be understood that the invention is not meant to be limited to the details disclosed therein. In the Examples, parts and percentages are by weight unless otherwise noted.

EXAMPLE 1--Preparation of 4"-cyanobenzylidene-4'-(N,N-di-n-hexylamino)-2-methyl-4-aminoazobenzene

A reaction mixture of 0.53 gram (3.5 millimols) of p-cyanobenzaldehyde, 0.79 gram (2 millimols) of 4'-(N,N-di-n-hexylamino)-2-methyl-4-aminoazobenzene, 150 ml of benzene and about 3 mg of p-toluenesulfonic acid was charged to a reaction vessel equipped with a magnetic stirrer and a reflux condenser topped with a graduated cylinder Claison adapter. The mixture was stirred at reflux until reaction had stopped as monitored by thin layer chromatography. The reaction mixture was filtered through a 150 gram silica gel bed and the product eluted with benzene. The solvent was removed by a flash rotary evaporator and the product purified by repeated column chromatography.

The product was recrystallized from hexane repeatedly until a thin layer chromotogram showed only a single spot.

4"-cyanobenzylidene-4'-(N,N-di-n-hexylamino)-2-methyl-4-aminoazobenzene having the formula ##STR4## was obtained in 72% yield (0.73 gram).

The structure was confirmed by elemental analysis: C calculated, 78.11%; Found, 78.29%; H calculated, 8.09%; Found, 8.14%.

This compound was orange-red in color and was monotropic, having a solid to nematic transition temperature of 94-95 C. and a melting point of 110.5 C.

EXAMPLES 2-11

Several additional compounds were prepared. The general procedure of Example 1 was followed, substituting the appropriate starting materials. Table 1 below summarizes the analyses, mesomorphic temperature ranges and colors of the dyestuffs obtained.

                                  Table I__________________________________________________________________________                           Analytical Data                           Car-                              Car-                           bon,                              bon,                                  H, H,           Mesomorphic                           calc,                              found                                  calc,                                     found                                         Yield    TemperatureEx.   Compound                     %  %   %  %   %   Color                                                  CN,C.                                                      NL,C.__________________________________________________________________________    ##STR5##                    74.79                              74.76                                  5.38                                     5.43                                         62  orange- red                                                  248 2523    ##STR6##                    75.59                              76.04                                  6.04                                     6.15                                         57  orange- red                                                  211 2554    ##STR7##                    75.94                              75.63                                  6.33                                     6.43                                         60  red  151.3                                                      103.3- 111.3*5    ##STR8##                    68.83                              68.72                                  5.74                                     5.57                                         78  red  235 2576    ##STR9##                    69.40                              69.54                                  6.02                                     6.18                                         64  red- brown                                                  164 120- 132*7    ##STR10##                   75.99                              75.60                                  5.54                                     5.55                                         33  red  187 2368    ##STR11##                   76.89                              76.59                                  7.09                                     7.16                                         37  orange- red                                                  72  1759    ##STR12##                   77.16                              77.54                                  7.32                                     7.46                                         68  orange- red                                                  54  12210    ##STR13##                   70.90                              70.70                                  6.78                                     6.77                                         38  orange- red                                                  84  18411    ##STR14##                   77.89                              78.02                                  7.91                                     7.84                                         51  orange- red                                                  88.5                                                      129__________________________________________________________________________ *monotropic-
EXAMPLE 12

The liquid crystal dyes prepared in Examples 1-11 were admixed with lower temperature mixtures of liquid crystals and the mesomorphic temperature ranges of the mixtures measured.

The Schiff base liquid crystal host contained 85% by weight of a 70:30 mol ratio of MBBA and EBBA and 15% by weight of p-ethoxybenzylidene-p'-aminobenzonitrile. This mixture has a nematic to isotropic liquid transition temperature of 63 C.

The ester liquid crystal host is available commercially from Hoffman-LaRoche as RO-TN-101 and is a mixture of three parts of p-cyanophenyl-p'-alkylbenzoates of the formula ##STR15## and one part of a p-phenylene-2,4-dialkylbenzoate of the formula ##STR16## wherein R', R" and R'", are alkyl groups.

The data are summarized below in Table II.

              Table II______________________________________                           Nematic to                           IsotropicCompound Host Liquid  Weight %  TransitionSample No.    Crystal      of Dye    Temperature,  C.______________________________________1        Ester        0.33      48-662        Ester        0.39      70.7-72.52        Schiff Base  0.228     31.53        Ester        0.34      70.7-71.53        Schiff Base  0.203     474        Ester        0.19      69-71.55        Ester        0.26      70-70.55        Schiff Base  0.287     526        Ester        0.23      70-71.27        Ester        0.26      70.5-728        Ester        0.4       62.54-658        Schiff Base  0.224     28.59        Ester        0.40      69.5-7110       Ester        0.38      70-7110       Schiff Base  0.204     2911       Ester        0.20      69-71.5______________________________________
EXAMPLE 13

A mixture of 0.21% of the liquid crystal dye of Example 11 in the ester host liquid crystal mixture of Example 12 was charged to a liquid crystal cell as in the FIGURE. The liquid crystal mixture was aligned in a direction parallel to the electrode of the cell. The optical density, as seen through plane polarized light parallel to the liquid crystal orientation, was measured at the visible absorption maximum (475 nm) as a function of applied voltage. The results are given below in Table III.

              Table III______________________________________Voltage(volts)            Optical Density______________________________________0                  0.4660.5                0.4661.0                0.4101.2                0.3641.5                0.3222                  0.2973                  0.2654                  0.2555                  0.2518                  0.24310                 0.24115                 0.23920                 0.237______________________________________

The results show that as the voltage is increased, the color fades.

EXAMPLE 14

A mixture of 0.34% of the dye of Example 3 in the ester host liquid crystal mixture of Example 12 was charged to a liquid crystal cell and optical density measured as in Example 13, except at 486 nm. The results are given below in Table IV.

              Table IV______________________________________Voltage (volts)     Optical Density______________________________________0                   0.8161                   0.6841.5                 0.6242                   0.473                   0.3544                   0.3295                   0.3198                   0.30110                  0.29815                  0.28920                  0.286______________________________________
EXAMPLE 15

A mixture of 0.19% of the dye of Example 4 in the ester host liquid crystal mixture of Example 12 was charged to a liquid crystal cell and optical density measured as in Example 13, except at 470 nm. The results are given below in Table V.

              Table V______________________________________Voltage (volts)     Optical Density______________________________________0                   0.5300.5                 0.5281                   0.5081.2                 0.3931.5                 0.3412                   0.3182.5                 0.2893                   0.2794                   0.2725                   0.26810                  0.26115                  0.25820                  0.257______________________________________
Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3597044 *Sep 3, 1968Aug 3, 1971Rca CorpElectro-optic light modulator
US3703329 *Dec 29, 1969Nov 21, 1972Rca CorpLiquid crystal color display
US3833287 *Mar 8, 1973Sep 3, 1974Bell Telephone Labor IncGuest-host liquid crystal device
US4032470 *Dec 22, 1975Jun 28, 1977Rca CorporationElectro-optic device
US4105654 *Nov 12, 1976Aug 8, 1978Rca CorporationLiquid crystalline 4"-cyano- or 4"-nitrobenzylidene-4'-(N,N-dialkylamino)-1-aminoazabenzene dyes
US4116861 *Aug 18, 1977Sep 26, 1978General Electric CompanyDichroic liquid crystal compositions
US4122027 *Nov 8, 1976Oct 24, 1978General Electric CompanyDichroic liquid crystal composition with 4,4-bis (substituted naphthylazo)azobenzene dichroic dyes
US4128496 *Sep 21, 1977Dec 5, 1978General Electric CompanyDichroic liquid crystal compositions
US4128497 *Jun 2, 1977Dec 5, 1978General Electric CompanyDichroic liquid crystal compositions
US4137193 *Jun 23, 1977Jan 30, 1979Bbc Brown, Boveri & Company, LimitedUtilization of dyes for liquid crystal displays
US4145114 *Jun 14, 1976Mar 20, 1979The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern IrelandPleochroic dyes
DE2627215A1 *Jun 18, 1976Jan 20, 1977Secr Defence BritFarbstoffe fuer fluessigkristallmaterialien
DE2631428A1 *Jul 13, 1976Jan 5, 1978Bbc Brown Boveri & CieVerwendung von farbstoffen
GB1459046A * Title not available
Non-Patent Citations
Reference
1 *Blinov, L. M., et al., J. Phys(Paris), vol. 36, c-1, (3), pp. 69-76 (1975).
2 *Bloom, A., et al., Mol. Cryst. Liq. Cryst., vol. 40, pp.213-221 (1977).
3 *Bloom, A., et al., Mol. Cryst. Liq. Cryst., vol. 41 (letters) pp. 1-4 (1977).
4 *Bloom, M., et al., k-12, Abstract of the 6th Int. Liq. Cryst. Conf., Kent, Ohio (Aug. 23-27, 1976).
5 *Constant, J., et al., "Pleochroic Dyes with High Order Parameter", presented at 6th Int. Liq. Cryst. Conf., Kent, Ohio (Aug. 23-27 1976).
6 *Uchida, T., et al. Mol. Crys. Liq. Cryst., vol. 24 (Letters) pp.153-158 (1977).
7 *Uchida, T., et al., Mol. Cryst. Liq. Cryst., vol. 39, pp. 39-52 (1977).
8 *White, D. L., et al., J. Appl. Phys., vol. 45, No. 11, pp. 4718-4720 (1974).
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4308161 *Aug 4, 1980Dec 29, 1981General Electric CompanyNovel yellow azo dyes and dichroic liquid crystal compositions made therewith
US4308162 *Dec 8, 1980Dec 29, 1981General Electric CompanyNovel yellow azo dyes and dichroic liquid crystal compositions made therewith
US4308163 *Aug 4, 1980Dec 29, 1981General Electric CompanyNovel yellow azo dyes and dichroic liquid crystal composition made therewith
US4308164 *Aug 4, 1980Dec 29, 1981General Electric CompanyNovel yellow azo dyes and dichroic liquid crystal composition made therewith
US4588517 *Jun 29, 1983May 13, 1986Hitachi, Ltd.Liquid crystal composition
US4600527 *Feb 10, 1983Jul 15, 1986Mitsubishi Chemical IndustriesLiquid crystal composition
US4737310 *May 19, 1986Apr 12, 1988Mitsubishi Chemical IndustriesLiquid crystal composition containing azo dyes
Classifications
U.S. Classification349/165, 252/299.64, 252/299.68, 252/299.1
International ClassificationC09B56/02
Cooperative ClassificationC09B56/02
European ClassificationC09B56/02